Plant reproduction

• What are flowering plants called?

  Angiosperms
• What are the male spores?


  Pollen grains produced in the anther
• What are the female spores?

  Embryo sacs produced in the ovule in the ovary
• What are hermaphrodites?

  Flowers or organisms that contain both male and female parts
• Anther

  • Contains four pollen sacs arranged in two pairs, side by side
  • When mature, the pollen sacs dehisce (open) and release pollen grains
• Carpel


  • A closed structure in which one or more ovules develop
  • The lower part surrounding the ovules is the ovary
  • At the tip of the carpel is the style, which ends in the receptive surface, the stigma
• Parts of a flower

  • Stamen
  • Anther
  • Filament
  • Sepal
  • Nectary
  • Receptacle
  • Petal
  • Stigma
  • Style
  • Carpel
  • Ovary
  • Ovule
  • Embryo sac
• The nectary produces nectar which is scented to attract pollinators
• What does the stamen consist of?

  • anther which produces the pollen grains
  • filament which supports the anther and contains vascular tissue and transports sucrose, mineral ions and water to the developing pollen grains
• What does the carpel consist of?

  • Stigma for receiving pollen grains
  • a style through which the pollen tube grows
  • ovaries containing ovules containing embryo sacs
• What is the calyx?

  The outermost ring of the flower consists of sepals to protect the flower
• What is the Corolla?

  A ring of petals inside the sepals which may have scented nectar at its base to attract pollinators
• What are the properties of insect pollinated flowers?

  • Large, brightly coloured petals
  • scent and nectar
  • Anthers and Stigma within the flower
  • small quantities of large, sticky sculptured pollen grains
• What are the properties of wind pollinated flowers?

  • Small green and inconspicuous petals
  • no scent or nectar
  • Anther and large feathery stigma hang outside flowers
  • large quantities of small smooth pollen
• What is the process of male gamete development?

  • diploid pollen mother cell undergoes meiosis in the pollen sacs to produce a tetrad containing four haploid cells
  • Each haploid cell undergoes mitosis to produce a generative nucleus and a pollen tube nucleus
  • The generative nucleus undergoes mitosis to produce two male nuclei
• What is the tapetum?

  A layer of cells around the pollen sac that provides nutrients and regulatory molecules to the developing grains
• What is the pollen cell wall?

  A tough and chemical resistant cell wall that resists desiccation, so the poles grains can be transferred from one plant to another without drying out
• What is dehiscence?


  When pollen is mature, the anthers dry out causing tension on the lateral grooves. The tension pulls the walls of the anther apart. An opening called the stomium exposes the pollen grains which are carried by the wind or by insects
• What do the ovaries contain?

  One or more ovule containing a mother megaspore cell
• Describe the development of female gametes

  • The megaspore cell undergoes meiosis to produce four haploid cells
  • Three of these disintegrate
  • The remaining cell undergoes three rounds of mitosis, producing eight haploid nuclei, one of which is the female gamete
• What does a mature embryo sac contain?

  • 1 oosphere
  • Two of the haploid nuclei fuse to produce a diploid polar nucleus
  • 3 antipodals
  • 2 synegrids
• What is the nucellus?

  A layer of cells that provide nutrients
• What does the embryo sac consist of?

  • nucellus
  • two layers of cells surrounding the embryo sac called the integuments
  • A gap in the integuments called the micropyle
• What is pollination?

  The transfer of pollen grains from the anther of one plant to the mature stigma of another plant of the same species
• What are the consequences of self-pollination?

  • Self-fertilised plants rely on crossing over and independent assortment and mutation to increase variation in their genomes so they display less genetic variation
  • Greater chance of two harmful gametes being brought together at fertilisation
  • An advantage is that successful genomes are preserved
• What are the consequences of cross pollination?

  • In addition to the events during meiosis and mutation, combination of gametes means there is more genetic variation
  • Reduced chance of two harmful alleles being brought together
  • Great evolutionary significance because some genomes are more successful than others which may allow species to survive
• How is cross-pollination ensured?

  • Protrandy- the stamen ripens before the stigma
  • Protogyny- the stigma ripens first
  • Anther below the stigma
  • Genetic incompatibility
  • Different flowers for male and female
  • Different male and female plants
• What is fertilisation?

  The fusion of male and female gametes to produce a zygote
• Double fertilisation

  1. Pollen grain lands on stigma and germinates in the sucrose to produce pollen tubes

  2. Pollen tube nucleus is at the tip of the pollen tubes with the two male nuclei behind it

  3. Pollen tube grows down the style up the gradient of chemoattractants e.g. GABA from the ovule

  4. The pollen tube nucleus produces hydrolases (protease and cellulase) to digest a path. Products used to grow the pollen tube

  5. Pollen tube grows through the micropyle and into the embryo sac

  6. Pollen tube nucleus disintegrates and pollen tube opens to release the two male nuclei

  7. One male gamete fuses with the oosphere to produce the zygote

  8. The other fuses with the diploid polar nucleus to produce a triploid nucleus called the endosperm nucleus
• What is the endosperm nucleus?


  A triploid nucleus that can repeatedly divide by mitosis to produce an endosperm tissue which takes over from the nucellus to provide nutrition for the developing embryo